This mod I'm planning/working on is pretty detailed; I'll describe my thoughts best I can. It's going to be a complete revamp of the Karma system in Wurm Unlimited, turning it from a reward system - "do these things, get points to spend on those things" - into more of a give-and-take system - "do good things, good things will happen; do bad things, bad things will happen".
First thing's first: every aspect of this mod will be configurable, and you can enable/disable individual features.
Player karma will support negative values to accompany this mod (the one thing that can't be disabled/adjusted with the mod installed and enabled)
A player's current karma "balance" (how many points you have) will have influence over the likelihood of rarity windows - high karma (above 0) would make them more likely, and low karma (below 0) would make them less likely. A zero karma would have no effect on the default behavior. Some kind of caps and checks in place to prevent weird stuff like 100% and 0% chances of course.
Each rarity window will reduce the player's karma (because it's a give-and-take system - you've "spent" your karma); perhaps a lesser amount subtracted for failed rare rolls vs. successful ones, and a setting to choose whether karma can fall below 0 when that takes place
Spending karma in the Karma menu (right-click body/inventory, choose Karma) requires you to have that much karma just like it does now; similar to a bank account, if you don't have enough karma for your "purchase" then you can't do it. So if your choice would cause your karma to fall to negative, you can't choose it and must earn more
Add ways to earn karma
Reward players with some amount for playing on the server, e.g. every 15 minutes spent active/online
Reward players once a day for logging in ("daily bonus")
Grant karma for prayers, sacrifices at altars, perhaps other "religious" actions
Reward players for burying corpses, destroying tree stumps, perhaps other "good" activities that would be beneficial to servers/communities
Spawn source crystals/fountains/springs randomly in the world; once tapped (all the karma has been "drank" by players) it is destroyed. Never on deeds, tiles with steep slopes, never on thorns/lava/other harmful tiles, never in caves, etc.
Achievements increase karma
Add ways to lose karma
The rarity windows as described above
Leaving corpses on the ground, chopping down trees and leaving the stumps behind, walking away from piles of items on the ground off-deed, harvesting crops without replanting them, etc.
Perhaps an option to lose some when you die, with or without the possibility to fall down to negative in this manner
Open to ideas for this one because I'm admittedly short on them compared to ways to earn karma
"Helper" functions for other devs to make use of that allow them to tie this karma system to their mods as well
Provide a /command or a window/action or something so players can see a "report" of things that have affected your own karma recently
e.g. You killed a ____ and left the corpse to rot
You earned the ____ achievement
You drank some source
You chopped down a ____ tree and left the stump behind
You harvested some ____ and didn't replant anything
You logged in; You earned a periodic bonus for playing; You prayed at an altar of ____; You sacrificed ____ to ____
I think that if properly setup so that server administrators can pick and choose the components they want to enable, this could be a very cool concept. I personally think the current karma system is more like a rewards system, which doesn't really embody the concept. But even just the functionality to grant karma for logins/periodically for time spent playing on the server could be of use to some servers even if they don't use any other feature of this mod.
It's obviously a pretty large-scale idea that I'm slowly hammering away at (I've got a day job! lol) but I'm hopeful I'll be able to release something eventually.
In the meantime, I'm open to feedback and suggestions; however, since I plan to make everything so customizable and don't intend to force any particular feature on anyone, I'm interested in hearing more ideas, not necessarily things that are wrong with existing ones other than if they're not really feasible/possible. (On that note, if I've got something planned that other modders could point out as impossible to code for reasons I haven't thought of, please speak up!)
Have a great day!